This theorem, along with re1luk11481 and re1luk21482 proves that tbw-ax11471,
tbw-ax21472, tbw-ax31473, and tbw-ax41474, with ax-mp8
can be used as a
complete axiom system for all of propositional calculus. (Contributed by
Anthony Hart, 16-Aug-2011.) (Proof modification is discouraged.)
(New usage is discouraged.)